Vena-Cava filters have been known and their use has been reported for more than twenty years, and the Review Article of Becker, et al., entitled "Inferior Vena Cava Filters--Indications, Safety, Effectiveness", Arch. Intern. Med.--Vol. 152, October 1992, acknowledges the commercial existence of at least six competitive varieties and provides an extensive bibliography of relevant papers. It suffices to indicate that these prior and current filter structures rely on guide-wire piloting techniques of installation but must be removed within 48 hours if they are not to become so trapped by tissue growth within the vein as to become potentially destructive of vein tissue should they be later removed. As a consequence, on many occasions, such filters have often had to stay in place, as a permanent fixture within the patient.
An expandable filamentary-mesh filter, made by Angiocor s.a.r.l. of Lille, France is an attempt to avoid this problem of wall-tissue growth, using mechanically actuated expansion of multiple helices, wherein the helices are of plastic filamentary material.
Other prior art vascular filter devices are disclosed in FR-A-2580504 and U.S. Pat. No. 4,662,885. Reference may also be made to U.S. Pat. No. 4,723,549 and EP-A-0377749.